Mitogen-activated protein kinase phosphatase-1
modulated JNK activation is critical for apoptosis
induced by inhibitor of epidermal growth factor
receptor-tyrosine kinase
Kenji Takeuchi
1
, Tomohiro Shin-ya
1
, Kazuto Nishio
2
and Fumiaki Ito
1
1 Department of Biochemistry, Faculty of Pharmaceutical Sciences, Setsunan University, Osaka, Japan
2 Department of Genome Biology, Kinki University School of Medicine, Osaka, Japan
Epidermal growth factor receptor (EGFR), a member
of the ErbB family, is important in the regulation of
growth, differentiation and survival of various cell
types. Ligand binding to EGFR results in receptor
dimerization, activation of its tyrosine kinase and
phosphorylation of its C-terminal tyrosine residues.
The tyrosine-phosphorylated motifs of EGFR recruit
various adaptors or signaling molecules [1,2]. EGFR
is able to activate a variety of signaling pathways
through its association with these molecules. The mito-
gen-activated protein kinase (MAPK) pathway leading
to phosphorylation of extracellular signal-regulated
Keywords
AG1478; c-Jun N-terminal kinase; epidermal
growth factor receptor; mitogen-activated
protein kinase phosphatase-1; non-small-cell
lung cancer

activated protein kinase phosphatase-1 (MKP-1), was constitutively
expressed in the PC-9 cells, and its expression level was reduced by
AG1478. The inhibition of JNK activation by ectopic expression of
MKP-1 or a dominant-negative form of JNK strongly suppressed AG1478-
induced apoptosis. These results reveal that JNK, which is activated
through the decrease in the MKP-1 level, is critical for EGFR-tyrosine
kinase inhibitor-induced apoptosis.
Abbreviations
EGFR, epidermal growth factor receptor; ERK, extracellular signal-regulated kinase; JNK, c-Jun N-terminal kinase; MAPK, mitogen-activated
protein kinase; MKP-1, mitogen-activated protein kinase phosphatase-1; NSCLC, non-small-cell lung cancer; PI, propidium iodide; PtdIns3-K,
phosphatidylinositol 3-kinase; SAPK, stress-activated MAPK.
FEBS Journal 276 (2009) 1255–1265 ª 2009 The Authors Journal compilation ª 2009 FEBS 1255
kinase (ERK) 1 ⁄ 2 plays an essential role in EGF-
induced cell growth; and the phosphatidylinosi-
tol 3-kinase (PtdIns3K) pathway is also important for
cell growth and cell survival. One way by which
PtdIns3K signals cells to survive is by activating pro-
tein kinase PDK1 which in turn phosphorylates Akt.
EGFR gene mutations or EGFR gene amplification
is detected in various types of malignancy [1,2]; there-
fore, EGFR-tyrosine kinase is a promising therapeutic
target. Orally active small molecules against EGFR
(e.g. gefitinib and erlotinib) show evident anti-tumor
effects in patients with various cancers, particularly
non-small cell lung cancer (NSCLC) [3–5]. Beneficial
responsiveness to EGFR-targeting chemicals in
NSCLC patients is closely associated with EGFR
mutations in the kinase domain [6–8].
The induction of apoptosis has been considered as a
major mechanism for gefitinib-mediated anti-cancer

through induction of the expression of JNK phospha-
tases, which include dual-specificity (threonine ⁄ tyro-
sine) phosphatases [26–28].
PC-9 cells are gefitinib-sensitive human NSCLC cell
lines with a mutation (delE746-A750) in their EGFR,
which allows the receptor to be autophosphorylated
independent of EGF. In this study, we investigated the
signaling route by which the EGFR tyrosine kinase
inhibitor AG1478 induces apoptosis in PC-9 cells.
There is a general agreement on the hypothesis that
the inhibition of ERK1 ⁄ 2 MAPK and ⁄ or PtdIns3K ⁄
Akt growth ⁄ survival signaling cascades leads to apop-
tosis of cancer cells. However, there are no studies
addressing the role of JNK in apoptosis induced by
EGFR tyrosine kinase inhibitors. Here, we demon-
strate that JNK-phosphatase MKP-1 expression is con-
trolled by a signal downstream of EGFR and that if
this signal is abolished by an inhibitor of EGFR tyro-
sine kinase, the decreased MKP-1 activity can result in
JNK activation, leading to the induction of apoptosis.
Results
We first examined the effect of AG1478 on the viabil-
ity of human NSCLC cell line PC-9. Treatment of the
cells with AG1478 markedly suppressed the cell viabil-
ity, as determined by the results of a colorimetric assay
(Fig. 1A). Photographic observation of AG1478-trea-
ted PC-9 cells revealed that AG1478 decreased the per-
centage of adherent cells in a time-dependent manner
(Fig. 1B). When AG1478-treated PC-9 cells were
stained with Hoechst–propidium iodide (PI), cells with

tion levels continued to increase for at least 24 h.
However, the activation of p38, another MAP kinase
sub-family member, was not evident up to 12 h after
AG1478 treatment; although an increase in the phos-
phorylation of p38 was detected at 24 h (Fig. 2C).
Phosphorylation of ERK1 ⁄ 2, prototypical MAPK, was
decreased by the treatment with AG1478 at the same
time as activation of JNK (data not shown).
Neither SB203580 nor PD98059, inhibitors of p38
and ERK1 ⁄ 2, respectively, affected AG1478-induced
apoptosis in PC-9 cells (data not shown), suggesting
that neither p38 nor ERK1 ⁄ 2 mainly transmit the
apoptotic signal of AG1478 in the PC-9 cells. If JNK
plays an important role in AG1478-induced apoptosis,
B
–
12 h
24 h
c
b
a
A
C
Fig. 1. Induction of apoptosis by AG1478. (A) PC-9 cells were
seeded into a 96-well microplate, and treated with AG1478 at vari-
ous concentrations for 48 h. The viability of cells was determined
by conducting WST-8 assays. The value of untreated cells was con-
sidered as 100% viability. The data presented are the mean ± SD
(n = 6). (B) PC-9 cells were seeded at a density 3 · 10
5

induced apoptosis. To test this scenario, we stably
transfected PC-9 cells with a mammalian expression
vector encoding a dominant-negative form of JNK,
and isolated two clones, J12A5 and J12B6. The results
of a JNK kinase assay confirmed that J12A5 cells had
no detectable activity (Fig. 3A). A colorimetric assay
for cell viability, microscopic observation of cells, and
an assay for caspase 3 activity revealed that this
dominant-negative kinase efficiently blocked AG1478-
induced apoptosis (Fig. 3B–D), indicating that activa-
tion of JNK mediated the AG1478-induced apoptosis.
A multitude of stimuli including osmotic stress acti-
vate JNK through phosphorylation of the JNK kinases
MKK4 and MKK7 [18,31]. To examine the mecha-
nism by which AG1478 induced JNK activation, we
incubated PC-9 cells in the presence of AG1478 for
several periods, and then prepared cell lysates from
these cells to determine the phosphorylation of MKK4
and MKK7 by immunoblotting (Fig. 4A). No phos-
phorylated MKK4 or MKK7 was observed in the
presence of AG1478, although phosphorylation of
both JNK kinases in response to osmotic stress could
be detected. Next, we determined the effect of AG1478
on the levels of MAPK phosphatases MKP-1 and
MKP-2. As shown in Fig. 4B, AG1478 decreased the
expression of the MKP-1 protein. As for the MKP-2
protein, however, AG1478 did not affect its expression
level.
To check the role of MKP-1 as an anti-apoptotic
signal molecule, we constitutively expressed MKP-1 in

mean of the triplicate samples, and the bar represents the standard
deviation. Similar results were obtained from three separate experi-
ments.
JNK activation is critical for AG1478-induced apoptosis K. Takeuchi et al.
1258 FEBS Journal 276 (2009) 1255–1265 ª 2009 The Authors Journal compilation ª 2009 FEBS
level of MKP-1 in M1A4 cells remained high, in con-
trast to that in PC-9 cells; although MKP-1 expression
was lowered once at 3 h after AG1478 treatment. JNK
phosphorylation was extremely low in M1A4 cells. The
expression patterns of MKP-1 and phospho-JNK seen
in M1A4 were also observed in M1B2 cells (data not
shown). The results of the JNK kinase assay indicated
that JNK was not activated in M1A4 cells, where the
MKP-1 expression level remained high even after
exposure to AG1478 (Fig. 5C).
We next tested whether the expression level of
MKP-1 correlated with sensitivity to AG1478. As
shown in Fig. 6A,B, overexpression of MKP-1 resulted
in resistance to AG1478. We also examined whether
AG1478 could activate the effector caspase 3 in M1A4
cells (Fig. 6C). In PC-9 cells, activation of caspase 3
was observed with a maximal increase (480%) at 24 h
after AG1478 treatment; however, in M1A4 cells, only
a slight increase in caspase 3 enzyme activity (28%
and 39% at 12 and 24 h, respectively) was detected.
These results show that the MKP-1 expression level
correlated with the susceptibility to AG1478-induced
apoptosis.
Discussion
Gefitinib, an EGFR-tyrosine kinase inhibitor, has been

MKK4 and MKK7 activation, parallel cultures were treated with
0.5
M sorbitol for 30 min or with 0.5 M sodium chloride for 15 min.
(B) The cellular lysates were prepared at the indicated time points
after AG1478 treatment. Total protein (40 lg) was subjected to
immunoblotting, and the membranes were hybridized with anti-
bodies against MKP-1 (upper) or MKP-2 (middle). The equal loading
of the samples was checked by using an antibody against a-tubulin
(lower). The experiments corresponding to (A) and (B) were
repeated three times with similar results.
A
B
C
Fig. 5. Expression of MKP-1 prevents JNK activation. (A) Cellular
lysates were prepared from parent PC-9 cells and pcMKP1- trans-
fected PC-9 cells (M1A4 and M1B2). The lysates were analyzed by
SDS ⁄ PAGE and immunoblotting with specific antibody against
MKP-1 (upper) or a-tubulin (lower). (B) Subconfluent PC-9 and
M1A4 cells were incubated with 500 n
M AG1478 for the indicated
times. The cells were then harvested, and equal aliquots of protein
extracts (40 lg per lane) were analyzed for phospho-JNK (upper)
and MKP-1 (lower) by immunoblotting. Each membrane was rep-
robed with JNK (upper) or an a-tubulin antibody (lower). Similar
results were obtained from three separate experiments. (C) Cell
lysates were prepared from PC-9 and M1A4 cells at the indicated
time points after treatment with 500 n
M AG1478. JNK activity was
determined as described in Experimental procedures. The experi-
ments were repeated three times with similar results.

cells. Taken together, our data indicate that JNK, but
not other MAPK family members such as p38 and
ERK1 ⁄ 2, mainly transmits the apoptotic signal of
AG1478 in the PC-9 cells.
JNK signaling can regulate apoptosis both positively
and negatively, depending on the cell type, cellular
context and the nature and dose of treatment [22,23].
Strong and sustained JNK activation is predominantly
associated with induction or enhancement of apopto-
sis, whereas transient JNK activation can result in cell
survival [23,24]. AG1478 induced strong and sustained
JNK activation in PC-9 cells (Fig. 2A,B). This finding
strengthens the possibility that JNK is a mediator of
the apoptotic action of AG1478.
JNK activity in cells is tightly controlled by both
protein kinases such as MKK4 or MKK7 and protein
phosphatases such as MKPs. MKP-1, the first member
of the MKP family to be identified as an ERK-specific
phosphatase, is also able to inactivate JNK and p38
[34–38]. MKP-1 is an immediate-early gene whose
expression is regulated by mitogenic, inflammatory
and DNA-damaging stimuli [39–41]. In this study,
we observed no activation of MKK4 or MKK7 in
AG1478-treated PC-9 cells (Fig. 4A). However, the
expression level of MKP-1, but not that of MKP-2,
A
B
C
Fig. 6. Expression of MKP-1 prevents AG1478-induced apoptosis.
A, PC-9, M1A4, and M1B2 cells were incubated with the indicated

tor PD98059 did not affect MKP-1 expression or acti-
vation of JNK in PC-9 cells (K. Takeuchi & F. Ito,
unpublished data), MPK-1 expression in PC-9 cells
may be controlled in an ERK-independent manner.
Recently, Ryser et al. reported that MKP-1 transcrip-
tion is regulated in the transcriptional elongation step:
under basal conditions, a strong block to elongation in
the first exon regulates MKP-1 gene transcription [45].
Thus, EGFR-mediated signals may overcome this
block to stimulate MKP-1 gene transcription in PC-9
cells. Another possible mechanism responsible for
EGFR-mediated enhancement of MKP-1 expression is
that MKP-1 degradation via the ubiquitin–proteasome
pathway is suppressed by EGFR activation. In fact,
some research groups have reported that the expression
level of MKP-1 is controlled via the ubiquitin–protea-
some pathway [46,47]. Our preliminary experiment also
indicated that AG1478-induced MKP-1 degradation
was suppressed in the presence of proteasome inhibitors
such as MG-132 and ALLN (K. Takeuchi & F. Ito,
unpublished data).
Gene disruption studies demonstrate that JNK is
required for the release of mitochondrial proapoptotic
molecules (including cytochrome c) and apoptosis in
response to UV radiation [48]. Bax and Bak (members
of the proapoptotic group of multidomain Bcl-2-related
proteins) are essential for the JNK-stimulated release of
cytochrome c and apoptosis [49]. Other studies have
shown that 14-3-3 proteins are direct targets of JNK
and that phosphorylation of 14-3-3 proteins by JNK

to gefitinib is important to identify patients who will
have a positive response to this drug. The EGFR gene
in tumors from patients with gefitinib-responsive lung
cancer was recently examined for mutations, and clus-
tering of mutations was detected in the part of the
gene encoding the ATP-binding pocket. Screening for
such mutations may identify patients who will have a
positive response to the drug. However, this study
showed that NSCLC cell line PC-9 was dependent on
the MKP-1 ⁄ JNK pathway for its growth and survival.
Thus, sensitivity to gefitinib may be predicted from the
detailed analysis of the MKP-1 ⁄ JNK pathway as
described in this study. Although the MKP-1 level in
normal cells is low, an increased level of MKP-1 has
been found in human ovarian, breast, and prostate
cancer [54–56]. Our results suggest that MKP-1 may
be a candidate drug target in order to optimize
gefitinib-based therapeutic protocols.
Experimental procedures
Materials
EGF (ultra-pure) from mouse submaxillary glands was pur-
chased from Toyobo Co., Ltd (Osaka, Japan). Fetal calf
serum came from Gibco (Grand Island, NY, USA). Phenyl-
methanesulfonyl fluoride, pepstatin A, aprotinin and
leupeptin were obtained from Sigma (St Louis, MO, USA).
RPMI-1640 medium was from Nissui Pharmaceutical Co.,
Ltd (Tokyo, Japan). Antibodies used and their sources were:
ERK1 ⁄ 2 (pT202 ⁄ pY204) phospho-specific antibody (clone
20A), JNK(pT183 ⁄ pY185) phospho-specific antibody
K. Takeuchi et al. JNK activation is critical for AG1478-induced apoptosis

supplemented with 5% fetal calf serum and used for all of
the experiments. PC-9 cells were plated 24 h before
transfection and co-transfected with 8.5 lg of pcDL-SRa
296JNK2(VPF) or pcMKP-1 and 1.5 lg of pBabePuro by
using the Lipofectamine reagent, and the transfected cells
were selected by exposure to 2.5 mg of puromycin (Sigma)
per mL of medium for 3 weeks. Empty vector and pBabeP-
uro were used for co-transfection as a negative control. The
expression of JNK protein and MKP-1 protein were
verified by immunoblot analysis using anti-(pan-JNK ⁄
SAPK1 aa264–415) and anti-(MKP-1) (Santa Cruz Biotech-
nology), respectively.
Determination of cell viability
The anti-proliferative effect of AG1478 on PC-9 cells was
assessed by using a Cell Counting Kit-8 (DOJIN, Kumam-
oto, Japan) according to the manufacturer’s instructions.
The Cell Counting Kit-8 is a colorimetric method in which
the intensity of the dye is proportional to the number of
the viable cells. Briefly, 200 lL of a suspension of PC-9
cells was seeded into each well of a 96-well plate at a den-
sity of 2000 cellsÆwell
)1
. After 48 h, the culture medium was
replaced with 100 lL of AG1478 solution at various con-
centrations. After incubation for 48 h at 37 °C, 10 lLof
WST-8 solution was added to each well, and the cells were
incubated for a further 40 min at 37 °C. A
450
was measured
using a Bio-Rad microplate reader model 550. Each experi-

by SDS ⁄ PAGE, after which they were transferred to an
Immobilon-P membrane (Millipore, Bedford, MA, USA)
for immunoblotting with antibodies.
Caspase 3 activity assay
Caspase activity was assayed as described previously [57].
Briefly, cells were lysed with buffer A, and the protein con-
centration in each sample was adjusted to 100 lgÆ50 lL
)1
of buffer A. Fifty microliters of 2· Reaction Buffer (0.2 m
Hepes ⁄ NaOH, pH 7.4, containing 20% sucrose, 0.2%
Chaps and 1 mm dithiothreitol) was added to each sample,
which was then incubated with Z-DEVD-AFC substrate
(50 lm final concentration) at 37 °C for 1 h. The samples
were read in a fluorometer (VersaFluor; Bio-Rad) equipped
with a 340–380 nm excitation filter (EX 360 ⁄ 40) and 505–
515 nm emission filter (EM 510 ⁄ 10).
JNK assay
PC-9 cells were cultured in RPMI-1640 supplemented with
5% fetal calf serum at a density of 6.0 · 10
5
per 100 mm
dish for 2 days and then assayed for JNK activity. JNK
assays were performed by using a SAPK ⁄ JNK Assay kit
(Cell Signaling Technology) according to the manufac-
turer’s specifications. In brief, after various times of treat-
ment with AG1478, adherent cells and floating cells were
harvested by centrifugation and washed once in NaCl ⁄ P
i
.
Subsequently, the cells were lysed with lysis buffer (consist-

Signaling Technology) and rotated overnight at 4 °C.
JNK–c-Jun complexes were collected and washed with lysis
buffer followed by kinase buffer, consisting of 25 mm
Tris ⁄ HCl, pH 7.5, 5 mm b-glycerophosphate, 2 mm Cle-
land’s reagent, 0.1 mm Na
3
VO
4
and 10 mm MgCl
2
. The
in vitro kinase reaction was initiated by the addition of
kinase buffer containing 100 lm ATP, samples were incu-
bated at 30 °C for 45 min, and reactions were terminated
by the addition of SDS sample buffer and heating to 95 °C
for 5 min. Phosphorylated c-Jun was detected by western
blotting using a phospho-specific c-Jun antibody (Cell Sig-
naling Technology).
Hoechst- PI staining
For the study of nuclear morphologic changes induced by
AG1478, PC-9 cells were seeded on coverslips, grown to
sub-confluence, and treated with AG1478 for the desired
times. After fixation with formalin solution, the cells were
stained with 10 lm Hoechst33342 and 10 lm PI in 5% fetal
calf serum ⁄ RPMI. Coverslips were mounted on slides by
using Dakocytomation Fluorescent Mounting Medium
(DAKO) and observed under a fluorescence microscope
(Axioskop; Carl Zeiss, Jena, Germany).
Acknowledgements
We thank Dr K. Shuai for providing the pbabePuro,

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FEBS Journal 276 (2009) 1255–1265 ª 2009 The Authors Journal compilation ª 2009 FEBS 1265